To check whether cleaning with alcohol the area where capillary glycaemia is determined affects its values.An intervention study.A nursing clinic in a Primary Care Health centre.300 adult diabetic patients were included. They were selected consecutively and allocated at random to one of three groups of 100. A different intervention was performed on each group, with application or otherwise of alcohol to the finger before the puncture to obtain capillary blood. The three groups were comparable in age and sex. Two determinations of glycaemia were performed consecutively on each patient (repeated measurements).There were no significant differences between the three groups in the repeated measurements.Applying alcohol to the fingers did not affect the determinations of capillary glycaemia in the third-generation measurers.